OpenAI’s staff is reportedly not happy about its board of directors firing founder and former CEO Sam Altman. According to a social media post from tech podcaster Kara Swisher, employees sent a letter to the board demanding that the members resign. The post states that 505 of the company’s 700 employees signed the letter.

OpenAI is the developer of the artificial intelligence (AI) chatbot ChatGPT, which boasts over 100 million active users, according to statistics site ToolTester.

Swisher posted a copy of the letter, which accuses the board of undermining the mission of OpenAI. “We, the employees of OpenAI, have developed the best models and pushed the field to new frontiers,” it states. But “the process through which you terminated Sam Altman and removed Greg Brockman from the board has jeopardized all of this work and undermined our mission and company.”

The letter suggests that “the most stabilizing path forward” would be “for [the board] to resign and put in place a qualified board that could lead the company forward in stability.”

Related: Who is Emmett Shear, OpenAI’s new CEO?

According to the letter, employees have attempted to investigate why Altman was fired but have been unable to get a clear answer from the board, which “has never provided any written evidence” to confirm its allegations.

The OpenAI board fired Altman on Nov. 17 for allegedly being “not consistently candid in his communications with the board.” Brockman was also removed as chair on the same day. Some investors quickly protested his removal and asked that he be reinstated. On Nov. 20, Microsoft CEO Satya Nadella announced that Altman and Brockman had been hired at Microsoft to head up a new AI team.